Deuteronomy 16:9-12

The Festival of Weeks Reviewed

9 You shall count seven weeks; begin to count the seven weeks from the time the sickle is first put to the standing grain.
10Then you shall keep the festival of weeks to the Lord your God, contributing a freewill-offering in proportion to the blessing that you have received from the Lord your God.
11Rejoice before the Lord your Godyou and your sons and your daughters, your male and female slaves, the Levites resident in your towns, as well as the strangers, the orphans, and the widows who are among youat the place that the Lord your God will choose as a dwelling for his name.
12Remember that you were a slave in Egypt, and diligently observe these statutes.